To connect a large number of batteries (cells) 110 for on-vehicle use in parallel or in series, as shown in FIG. 11, the adjoining batteries 110 are electrically connected via bus bars 2 which are made of a metal plate and welded to the electrodes of the batteries 110 for connection. The bus bars 2 are thus connected to the electrodes of the respective batteries 110 and between the electrodes of the adjoining batteries 110. Charging voltages to the respective batteries 110 and the values of currents flowing between the batteries 110 can be obtained from the bus bars 2. Jumper plates 102 made of a metal plate are then electrically connected to the bus bars 2. Via the jumper plates 102, the bus bars 2 are electrically connected to sensors for monitoring the state of the voltages and currents of the batteries 110 and patterns of circuit boards 111 on which the sensors are mounted.
Since a high current flows through the bus bars 2, the connection of the bus bars 2 and the jumper plates 102 has a risk of heat generation if the electrical connection is made with a high contact resistance. Moreover, since the bus bars 2 and the jumper plates 102 are mounted on a vehicle and are likely to undergo vibrations over a long period, the bus bars 2 and the jumper plates 102 therefore need to be firmly fixed to each other at a high contact pressure. A connection structure 100 between a bus bar 2 and a jumper plate 102 is obtained as follows. Respective insertion holes having the same outline are formed in the bus bar 2 and the jumper plate 102. The bus bar 2 and the jumper plate 102 are stacked, and a bolt 103 or a screw is inserted through the coaxially-communicating through holes. Then, the bus bar 2 and the jumper plate 102 are fastened together between the bolt 103 or screw and a nut 104 so that the bus bar 2 and the jumper plate 102 are firmly fixed to each other and electrically connected at a high contact pressure (Patent Literature 1 and 2)